This invention relates to a lid for a can-shaped container and more particularly to a lid to be connected to a peripheral wall of a can-shaped container or can for holding beverage, such as coffee and juice, soup, solid foodstuffs, etc., the lid being made predominantly of a synthetic resin instead of metal and being openable without any tool such as a can opener. More specifically, the invention relates to an improved score portion enabling the opening of the can.
The present inventors have heretofore made various proposals with respect to lids of the type described above which are adapted to connected to a peripheral wall of a can-shaped container and are made predominantly of a synthetic resin.
One example of such lids will now be described with reference to FIG. 7(D). A lid 1A for a can-shaped container comprises a can-shaped container lid base 2 which comprises a multi-layer base of the gas barrier type and has a bottom 2A, an upstanding portion 2B extending from the outer periphery of the bottom 2A, and a flange 2C extending outwardly from the upstanding portion 2B in substantially parallel relation to the bottom 2A; a thermoplastic resin layer 3 which extends from the outer peripheral edge portion of the upper surface of the bottom 2A, facing away from the other side thereof to be connected to the peripheral wall of the can-shaped container, to the outer end of the flange 2C, and further projects from the outer end of the flange 2C downwardly in substantially parallel relation to the upstanding portion 2B in a direction opposite to the upstanding direction thereof; a tab seat 5 of a synthetic resin formed on that portion of the upper surface of the bottom 2A of the base 2 surrounded by the thermoplastic resin layer 3 in such a manner that there is provided a space 4 between the tab seat 5 and the upper surface of the bottom 2A; and a tab 6 connected at one end to the tab seat 5. The can-shaped container lid 1A has a score portion 7 formed between the outer periphery of the tab seat and the inner peripheral edge of the thermoplastic resin layer 3, the upper surface of the bottom 2A of the base 2 being exposed through the score portion 7.
For example, the lid 1A for a can-shaped container is manufactured as follows. As shown in FIG. 7(A), there is prepared the can-shaped container lid base 2 which has the bottom 2A, the upstanding portion 2B and the flange 2C as described above. Then, as shown in FIG. 7(B), the thermoplastic resin layer 3 is formed so as to reinforce at least the upstanding portion 2B and flange 2C of the base 2. Then, as shown in FIG. 7(C), the tab seat 5 formed on the upper surface of the bottom 2A in such a manner as to form the space 4 and the score portion 7, and the tab 6 is connected to the tab seat 5 to provide the lid 1A for a can-shaped container as shown in FIG. 7(D).
In this case, it is possible that the tab 6 is connected to the tab seat 5 beforehand, and that the thermoplastic resin layer 3 is formed after the tab seat 5 with the tab 6 is connected to the base. Anyway, one of the features of the present invention is to make the width (S) of the score portion 7 (see FIG. 7(C)), formed between the outer periphery of the tab seat 5 and the inner peripheral edge of the thermoplastic resin layer 3, as small as possible.
FIG. 8 is a plan view of the lid 1A for a can-shaped container, and FIG. 9 is a perspective view showing one example in which the can-shaped container lid 1A is mounted on a peripheral wall 8 of the can-shaped container body.
Although for illustration purposes, the can-shaped container lid base 2 used in the can-shaped container lid 1A is cross-sectionally shown as one layer in FIG. 7, using a hatching representative of a resin, the base 2 actually comprises three layers, that is, an inner base layer 200 of the gas barrier type shown as a metal foil, and a pair of thermoplastic resin layers 201 and 202 formed respectively on the opposite sides of the inner base layer as shown in FIG. 6.
As later described, the present inventors have earlier developed a molding method in which the three-dimensional base 2 for a can-shaped container lid, as shown in FIG. 7(A), can be molded without producing any pinholes. Therefore, it is possible to reduce the thickness of the base 2.
For opening the can-shaped container lid 1A, the tab 6 is pulled up as indicated by an arrow in FIG. 7(D), so that the score portion 7, through which the thin base 2 is exposed, is cut to thereby open the can.
FIG. 10 is a plan view of the lid 1A after it is opened, and FIG. 11 is a cross-sectional view taken along the line XI--XI of FIG. 10, showing the lid 1A and the peripheral wall 8 of the can-shaped container after the opening of the can.
Thus, the lid 1A is opened by cutting the score portion 7. If the width (S) of the score portion 7 is too large, the base 2 is liable to be extended due to the stress developing at the time of the opening of the can, thereby greatly lowering the degree of easy opening.
In view of this, in the lid 1A, the tab seat 5 is provided as a separate element, and is connected to the upper surface of the bottom 2A of the base 2 so as to make the width (S) of the score portion 7 as close to zero as possible.
When the width (S) of the score portion 7 is thus made as close to zero as possible, the risk of introducing or injecting a foreign matter into the container through the thin base 2 can be prevented, thus providing an improved tamper resistance.
In such a lid, the easily-opening ability and the rupture strength of the can are those characteristics which are contradictory with each other. When it is intended to improve one of these characteristics, the other characteristic often tends to become unsatisfactory. Thus, such a difficult problem has heretofore been involved in providing a can-shaped container having such a synthetic resin lid which is openable without the use of any tool such as a can opener.
Generally, it is considered that the narrower the width of the score portion 7 is, the greater resistance to withstand a breakage or rupture of the can is obtained. However, the reverse is the case. The greater width the score portion 7 has, the more energy is absorbed when the can is dropped, thus achieving a greater rupture strength.
Anyway, it is necessary for the lid to have a tamper resistance, an easily-opening ability and an increased can rupture strength. In the lid 1A, there is provided the space 4 between the upper surface of the bottom 2A of the can-shaped container lid base 2 and the tab seat 5 in order to increase that portion of the base 2 which can absorb the energy developing when the can is dropped, thereby relieving the concentration of the impact on the score portion 7 when the can is dropped.
In the above lid, even if the width (S) of the score portion 7 is made as close to zero as possible, the score portion is still exposed as shown in FIG. 7(D) (cross-sectional view) and FIG. 8 (plan view). As a result, dirt and the like tend to collect in the score portion 7. This is not only insanitary but also may cause the score portion 7 to be easily damaged. Therefore, it is desirable from this point of view and also from the viewpoint of a tamper resistance that the score portion 7 is not exposed.
In this connection, Japanese Laid-Open (Kokai) Patent Application No. 163641/82 discloses an easily-openable sealing lid of a plastics material for a container which has an upwardly-exposed score portion.
In such a construction, also, dirt and the like tend to collect in the score portion, which is insanitary when the lid is opened, and it is desirable from this point of view and also from the viewpoint of a tamper resistance that the score portion is not exposed.